﻿#include <stdio.h>
int main(void)
{
    int n;
    double sum, a, b, c;
    sum = 0;
    b = 1.0;
    c = 1.0;
    scanf_s("%d", &n);
    for (int i = 1; i <= n; i++) {
        a = b;
        b = b + c;
        c = a;
        sum = sum + b / c;
    }
    printf("%.2lf\n", sum);

    return 0;
}